I finally got the problem solved. I was having so much trouble getting audio to work correctly with jack/asla/pulse... that I started over. I reinstalled kxstudio, erasing the harddrive and it looks like all my audio problems cleared up.
So you are not the problem after all Jules.
But now I have a juce-jack question. I start my mixer application, and in the audio settings I select jack and system for for input and output the click the channels to use. (There are 18 in and 20 out to choose from) This works and my mixer gets input and output from my usb device. But what I see in the catia (jack routing) window has me confused.
2 devices get added, JuceJack that has 18 in/20 out. This matches the scarlett 18i20 interface for number of i/o. But why? The mixer can have more or less inputs than that so how do the number of channels get set for the jucejack device?
The second device is JackJuce-1 and it has 5 sets of 18 inputs and 5 sets of 20 outputs, but has the same number of inputs automatically routed as JuceJack. I don't understand why there are 2 JuceJack devices and why does the second one have 5 times as many ins and outs?